General security systems in an airport or the like can check belongings from the image of a human body to which X-rays has penetrated. It is difficult even in a short time to avoid exposure to X-rays. Furthermore, metal detectors can check metals. However, there are problems in that the metal detectors can check only a relatively large material and cannot specify a material inside the human body or materials other than metals. A method for checking materials in addition to metals using terahertz waves is spreading as a relatively new method. However, there are problems in that the terahertz waves cannot check the inside of a human body although can penetrate a material like clothes, and in that the reflection of the terahertz waves on the surface of the human body raises a privacy issue because showing the body shape.